Alsthom's French Pat. No. 2,071,299 describes valves satisfying the same requirement, comprising a moving baffle which tilts about a horizontal shaft and is actuated by an adjustable-ballast float.
Such valves have the following disadvantages: they make it necessary to select the operating mode (regulation either of the upstream level or the downstream level) on a permanent basis; and require that the level to be kept constant also be set permanently, said level setting being impossible or very difficult to modify.
Preferred embodiments of the present invention provide an automatic level sustaining valve or sluice gate enabling the changeover from regulation of the upstream level to regulation of the downstream level to be easily accomplished and also enabling the set point to be adjusted, both either manually or by remote control by means of a low-level signal transmitted, for example, via a telephone line.